Contraceptive methods include medications, intrauterine devices (IUDs), surgery (e.g., vasectomy, tubal ligation), spermicides, barriers (e.g., condoms), and "natural" methods. Only condoms protect against sexually transmitted diseases (STDs).
The so-called natural contraceptive methods are not very effective. However, without other means to control pregnancy, these have to be used. They include the abstinence, withdrawal, breastfeeding, temperature measurement, mucous, and counting days (rhythm) methods.
Abstinence is hard to sustain and therefore doesn't work. Withdrawal is not much better, since the male often does not withdraw in time, or even know exactly when to withdraw. Breastfeeding often protects a woman from pregnancy in the first 6 months after delivery if she has not had menses, feeds the child nothing other than breast milk, and never goes more than 6 hours between breastfeedings. The temperature measurement method relies on keeping track of very small temperature changes over time, so is unlikely to be useful in austere situations.
The mucous method requires the woman to check her vaginal mucous every day, at the same time, before she has intercourse. She wipes her vagina with a clean finger, paper, or cloth. If the mucous is clear, wet, and slippery, it means that she is fertile and should not have intercourse. If there is no mucous or if it is white, dry, and sticky, intercourse is probably safe two days later. If using this method, the woman should not douche or wash her vagina. The method is completely useless in the presence of vaginal infections.1
The counting or rhythm method is somewhat effective for women with a regular menstrual cycle of 26 to 32 days. Counting from the first day of menstrual bleeding, she abstains from sex from the 8th day through the 19th day of her cycle. She can have sex again on the 20th day. Women should use a chart to mark these days or, as an alternative, a bead chain with different colors. Each bead designates 1 day. To make a bead chain, string 32 beads on a string in this order: 1 red bead followed by 6 blue beads, 12 white beads, and 13 more blue beads. Use a small string or rubber grommet to mark where she is in her cycle. The red bead marks the onset of menses. The 6 blue beads are "safe" days for sex, as are the other 13 blue beads. The white beads are her fertile days.2
Male and female condoms are both successful contraceptive methods, but they cannot be improvised. Buy them! They also have medical uses as described elsewhere in the book (e.g., controlling postpartum hemorrhage, as ultrasound probe covers, improvising esophageal stethoscopes, and so forth).
Even in austere circumstances, emergency contraception may be an important issue. The medication of choice after unprotected sexual intercourse ...